An image forming apparatus includes a plurality of sheet sensors in a sheet path. The sheet sensors represent a paper feed sensor, a resist sensor, a paper ejection sensor, and the like. The image forming apparatus determines timings of image forming by outputs of the sheet sensors. The image forming apparatus detects the occurrence of jamming by the respective sensor outputs.
The image forming apparatus always supplies electric power to the sheet sensors. The various sheet sensors are supplied with electric power irrespective of whether they are to transport a sheet or not. The image forming apparatus requires energy saving.
Conventionally, there is known an image forming apparatus which is configured to achieve electric power saving. The image forming apparatus prevents electric power supply to the sheet sensors. When the image forming is not performed, the image forming apparatus turns off power sources used when the image is formed.
As an example of how to realize electric power saving, when the temperature of a fixing unit does not reach a regulated temperature, an image forming apparatus is known which stops the electric power supply to the sheet sensors used when the image is formed.
However, in an operation (printing) during image forming, the image forming apparatus turns on the power sources of the sheet sensors so that they are on all the time. In the printing operation, the image forming apparatus requires the largest electric power. The image forming apparatus cannot reduce the electric power in the printing operation.
The image forming apparatus cannot reduce the output capacity of a low voltage power supply unit required for the apparatus. The low voltage power supply unit represents electric power sources to an electrical circuit substrate, motors and sensors. The image forming apparatus cannot reduce the cost due to the low voltage power supply unit. The image forming apparatus has a problem in that the electric power saving in the printing operation cannot be achieved.